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Hello all ... I'm a newbie and just purchased this unit. I know it is currently setup for NG at 208V-3P and runs perfectly as such. It was highly maintained by the company I work for since new. It has very low loaded hours. It is in excellent condition with only typical oil leaks at the front main seal and valve cover gasket It is a little dirty now but was very clean prior to recent construction in the area. The serial number is 0571300010.
I want to convert to LPG and 120/240-1P. As I learn from info found here:
The unit is a 1957 model.
It will easily retap to 120/240-1P - assuming I can locate manuals/instructions.
The NG to LPG conversion appears to be a simple matter of retuning the mixer.
If any of that is wrong, please correct me.
QUESTION - The original transfer switch is available. Should I pay to have it removed/bypassed (~$250) for my use or should I just buy a new modern TS?
If you have manuals I will greatly appreciate any and all info.
GREAT SITE HERE GUYS!!! THANKS!

If the engine is equipped with an Impco carburetor, you will need to install a negative-feed (demand) regulator upstream of the carburetor to run LP-Gas. A "standard" Impco carburetor handling LP-Gas (Propane) fuel requires a negative 1.5-inch water column gas inlet pressure (a vacuum). Natural gas, in contrast, is fed to the Impco carburetor at positive 5 inches water column.

If the engine is equipped with an Impco carburetor, you will need to install a negative-feed (demand) regulator upstream of the carburetor to run LP-Gas. A "standard" Impco carburetor handling LP-Gas (Propane) fuel requires a negative 1.5-inch water column gas inlet pressure (a vacuum). Natural gas, in contrast, is fed to the Impco carburetor at positive 5 inches water column.

Huh?????

I would like for you to elaborate some on the information you posted above. I would like to find out more about "negative feed" regulators.

ChapinGuy - The "Imp" (or Maxitrol) regulator shown in your picture three is what you need to change from natural gas configuration to propane gas configuration. Your "Imp" regulator is installed with the spring tower pointing down toward the ground. For natural gas operation, the spring inside the tower is adjusted to provide a nominal 5 inch water column positive pressure at the carburetor gas inlet. For propane gas operation you unscrew the cap on the tower and remove the spring from the tower. This causes the "Imp" to function as a negative-feed regulator and it will yield a nominal 1 inch water column negative (vacuum) pressure at the carburetor gas inlet. The "Imp" has to be installed with the spring tower pointing down to do this.

Max - A negative feed regulator is a demand regulator. It does not allow gas to flow to the carburetor until a vacuum signal is applied on the outlet of the regulator. When the engine is running the fuel gas pressure to the carburetor is below atmospheric pressure, therefore, a negative pressure. The well known Garretson KN is another example of a negative feed regulator. The nominal setpoint on the KN is negative one-half inch water column.

The difference between the Impco and Garretson regulator settings relate to the respective carburetor designs. The KN is applied with a venturi type carburetor, while the Impco carburetors are an air valve design. The vacuum signal derived by a venturi carburetor is relatively weak, compared to the vacuum signal derived by an air valve carburetor.

Do not confuse a vacuum-operated fuel lock device with a negative feed regulator. They are not the same. A vacuum fuel lock is operated by intake manifold vacuum. A demand regulator is responding to carburetor venturi vacuum. These two vacuum signals are very different from one another.